Zk学习笔记——创建节点

参考:从Paxos到Zookeeper分布式一致性原理和实践

使用的zk依赖是cdh5.16.2的3.4.5

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<!-- zookeeper -->
<dependency>
    <groupId>org.apache.zookeeper</groupId>
    <artifactId>zookeeper</artifactId>
    <version>3.4.5-cdh5.16.2</version>
</dependency>

Zk在创建节点的有同步创建和异步创建,但是Zk是不支持递归创建节点,即父节点必须存储。

在创建同名的节点的时候,会抛出NodeExistsException异常。

Zookeeper节点内容只支持字节数组(byte[])

同步创建节点代码,其中创建了一个永久节点,key是/app1,value是123

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package com.bigdata.zookeeper;
 
 
import org.apache.zookeeper.*;
import java.util.concurrent.CountDownLatch;
 
public class ZkExample implements Watcher {
 
    public static CountDownLatch connectedSemaphore = new CountDownLatch(1);
 
    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper("master:2181", 5000, new ZkExample());
        System.out.println(zk.getState());
        try {
            connectedSemaphore.await();
            String path = zk.create("/app1", "123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE, CreateMode.PERSISTENT);
            System.out.println("success create znode: " + path);
        } catch (InterruptedException e) {
            System.out.println("Zk session established" + e);
        }
    }
 
    @Override
    public void process(WatchedEvent watchedEvent) {
        System.out.println(watchedEvent);
        if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
            connectedSemaphore.countDown();
        }
    }
}

输出,使用Zkui查看zk中的数据,能发现多出了/app1的节点,节点的值是123

 

Zk中节点的类型分为持久节点(PERSISTENT),持久顺序节点(PERSISTENT_SEQUENTIAL),临时节点(EPHEMERAL),临时顺序节点(EPHEMERAL_SEQUENTIAL)

区别如下

异步创建节点代码,

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package com.bigdata.zookeeper;
 
 
import org.apache.zookeeper.*;
 
import java.util.concurrent.CountDownLatch;
 
public class ZkExample implements Watcher {
 
    public static CountDownLatch connectedSemaphore = new CountDownLatch(1);
 
    public static void main(String[] args) throws Exception {
        ZooKeeper zk = new ZooKeeper("master:2181", 5000, new ZkExample());
        System.out.println(zk.getState());
        try {
            connectedSemaphore.await();
            zk.create("/app2", "123".getBytes(), ZooDefs.Ids.OPEN_ACL_UNSAFE,
                    CreateMode.PERSISTENT, new IStringCallback(), "This is context");
            Thread.sleep(Integer.MAX_VALUE);
        } catch (InterruptedException e) {
            System.out.println("Zk session established" + e);
        }
    }
 
    @Override
    public void process(WatchedEvent watchedEvent) {
        System.out.println(watchedEvent);
        if (Event.KeeperState.SyncConnected == watchedEvent.getState()) {
            connectedSemaphore.countDown();
        }
    }
}
 
class IStringCallback implements AsyncCallback.StringCallback {
 
    @Override
    public void processResult(int i, String s, Object o, String s1) {
        System.out.println("Create path result : [" + i + ", " + s + ", " + o + ", real path name : " + s1);
    }
}

如果创建成功,返回的状态码是0

 

如果节点已经存在,返回的状态码是-110

具体介绍

 

posted @   tonglin0325  阅读(1564)  评论(0编辑  收藏  举报
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